Best practice for expansion planning?

[shockking]

I'm looking for a good citable reference procedure for expansion planning. A typical scenario is: electrifying a facility, replacing NG boilers with electric boilers, therefore significantly increasing the electric load. There is typically one transformer feeding a single main switchboard. There is also typically good reliable meter data showing the peak demand (and therefore how much additional load could be supplied by the existing transformer). Anything come to mind? Thanks.

 

[petersonra]

If you know there are loads to be added at a later date and what they are you can accommodate them.

On the other hand, the customer might not want to pay for it until the conversion actually happens.

I don't think there are any real rules for this kind of thing.

Rather than having to replace the main switchboard or the main transformer, it might be more cost effective to just add on to what is already there.

Maybe you end up with 2 or 3 additional service xfmrs and some fused disconnects for them, and leave what is already there as is.

 

[shockking]

Aw should have clarified. This is for existing buildings with existing transformers and panels, and we are making plans to expand the electrical service (if needed) in order to retrofit/replacing existing gas boilers with electric boilers. I'm looking for a procedure/best practice for evaluating how much additional load can be added to this existing electrical service; or if the service is insufficient, best practice for increasing the capacity.

For example, would you expect to be better off replacing the existing transformer or adding a second transformer?

From our internal discussions, it sounds like for most cases at our facility, replacing the existing transformer with a larger one will be the typical solution (plus whatever other conductor/panel upsizing for each building).

I'm just curious if there's any industry references I should be familiar with?

 

[petersonra]

The load calcs will tell you how much additional load what you already have can handle.

I'd be inclined to leave what is there as is other than adding load(s) if possible. If it is working why screw with it.

If you need more load than what is available, I would be inclined to add another transformer.

I don't know of any industry norms that cover possibly maybe adding future loads.

 

[electrofelon]

I don't think there are any standards or best practices. There are just too many variables. Sometimes it's going to be leaving the existing and adding another set of new, sometimes it's going to be bringing in a new service sometimes the same voltage sometimes a different voltage, it's going to depend on utility construction costs, physical layout of everything, etc.....

The one thing that I can think of that will offer you some guidance is the NEC rules on number of services which is generally one with exceptions. Also I'm guessing most utilities will want to serve you with one transformer rather than multiple if possible.

 

[gadfly56]

I don't think there are any standards or best practices. There are just too many variables. Sometimes it's going to be leaving the existing and adding another set of new, sometimes it's going to be bringing in a new service sometimes the same voltage sometimes a different voltage, it's going to depend on utility construction costs, physical layout of everything, etc.....

The one thing that I can think of that will offer you some guidance is the NEC rules on number of services which is generally one with exceptions. Also I'm guessing most utilities will want to serve you with one transformer rather than multiple if possible.

I'm sure that's true, but I've seen several threads where posters have complained that the POCO won't install a transformer large enough to accommodate planned expansions. I would guess the best you can do is make sure that wherever the transformer lives that it can accommodate a larger one in the future.

 

[electrofelon]

I'm sure that's true, but I've seen several threads where posters have complained that the POCO won't install a transformer large enough to accommodate planned expansions. I would guess the best you can do is make sure that wherever the transformer lives that it can accommodate a larger one in the future.

I don't know the details of those discussions you are referring to, but in my experience when you are designing an electrical service you give the power company the loads, and you are free to give them whatever loads you want - they certainly are not going to audit or verify them. And of course many people frequently think the utility transformer is too small

 

[shockking]

Thanks all, I appreciate the sanity check

The one thing that I can think of that will offer you some guidance is the NEC rules on number of services which is generally one with exceptions.

FYI for others, Looks like NEC section 230. The exceptions are basically for special cases (e.g. fire pumps, emergency power) and if the building or load is so large that it warrants multiple transformers.

Also I'm guessing most utilities will want to serve you with one transformer rather than multiple if possible.

For what it's worth, this is a college campus. Our only utility connection is 115 kV at our own substation. Downstream at individual buildings, save for a few exceptions, we don't have to worry about what the utility wants

I don't know the details of those discussions you are referring to, but in my experience when you are designing an electrical service you give the power company the loads, and you are free to give them whatever loads you want - they certainly are not going to audit or verify them. And of course many people frequently think the utility transformer is too small

Quick tip: At least here with PG&E, I was advised to request the largest transformer feasible for the panel and save the documentation; PG&E will size and install whatever transformer they see fit, but as long as you have the documentation showing your request called for a larger transformer, they will upsize it at no cost if/when the need arises.